A combustor of a gas turbine includes a transition piece that sends high-temperature and high-pressure combustion gas to a turbine.
A body wall forming the transition piece has a structure that guides cooling air into the body wall in order to prevent the burnout of the transition piece. Specifically, a plurality of cooling air passages, which extend in the axial direction of the transition piece, are formed in the body wall, and a cooling air inlet port opened to the outer circumferential surface of the body wall and a cooling air outlet port opened to the inner circumferential surface of the body wall are formed at each of the plurality of cooling air passages. Cooling air is introduced into the cooling air passages from the cooling air inlet ports, and flows into the transition piece from the cooling air outlet ports.
The cooling air outlet port, which is formed at each of the plurality of cooling air passages, is often formed at the same position in the axial direction of the transition piece. In order to increase thermal efficiency, a gas turbine in recent years has been designed so that the temperature of combustion gas flowing in the transition piece is higher than that in the past. In the transition piece, the number of the cooling air passages is increased and a distance between adjacent cooling air passages is reduced more than that in the past to improve the cooling effect of the body wall.
Cracks tend to occur in the body wall of the transition piece from the cooling air outlet ports first, where the thermal environment is severe and stress is apt to be concentrated. In addition, when a distance between the cooling air passages is reduced than that in the past as described above, the distance between adjacent cooling air outlet ports is also reduced. Accordingly, when a crack occurs in the body wall from a certain cooling air outlet port first, the crack is apt to be connected to the next cooling air outlet port. As a result, the growth of the cracks is facilitated.
Japanese Unexamined Utility Model Application, First Publication No. S62-150543 discloses that cooling air outlet ports of a plurality of cooling air passages are arranged so as to be staggered. When the cooling air outlet ports are arranged in this way, since the positions of the adjacent cooling air outlet ports are different from each other in the axial direction of the transition piece, even if a distance between the adjacent cooling air passages is reduced, the distance between the adjacent cooling air outlet ports is ensured so as to be larger than the distance between the cooling air passages. Therefore, even if a crack occurs from a certain cooling air outlet port first, it is possible to suppress the growth of the cracks to some extent.